Manufacture of carbon cloth from polymeric fibre material



United States Patent Us. or.- 23-2091 6 Claims ABSTRACT OF THE DISCLOSURE According to the invention, polymer fibers, for example polyacrylonitrile fibers, are oxidized by heating them in an oxidizing atmosphere at a temperature within the range of 100-250 C. while held under tension, the oxidized fibers are woven by a conventional weaving process to provide a woven cloth of oxidized yarns, and, the woven cloth of oxidized yarns is carbonized by heating in a non-oxidizing atmosphere up to a temperature in the region of 1000 C. to provide carbon fiber cloth.

This invention relates to carbon fibre cloth and processes for its manufacture. It is to be noted that as used in this specification the term carbon may include graphite.

Carbon and graphite cloth is known and in one exam pie is made by carbonising woven fabric of staple rayon fibres. In a typical example the carbon cloth has a tesnile strength of about 25 lb./inch width and individual fibers extracted from the carbon cloth have a tensile strength of about 50 1O 1b./ sq. inch and have a Youngs modulus of 59 10 lb. per sq. inch.

Carbon fibres of high Youngs modulus and high tensile strength characteristics have been produced from fibers of polymeric material for example polyacrylonitrile as disclosed in co-pending US. application Ser. No. 449,320, now Pat. No. 3,412,062 and polyamide, polyester and polyvinyl alcohol as disclosed in copending British application Ser. Nos. 28,108/65 and 13,232/66 now cognated in British Pat. No. 1,166,251. Processes for their manufacture in continuous lengths are disclosed in copending US. application Ser. No. 648,916. However, attempts to fabricate such carbon fibres into a carbon cloth, for example by conventional weaving methods,

a have not so far proved successful the fibres breaking during manipulation.

The present invention is concerned with the production of a high strength carbon fibre cloth from polymeric fibre material of a type in which the linear molecules can be cross-linked, for example by oxidation by heating at below their melting point in an oxidizing atmosphere, in particular polyacrylonitrile or, if the polymer is of a type having no melting point, heating in an oxidizing atmosphere at a' temperature which allows oxidation to proceed in a controlled manner, and which upon subsequent carbonising in a non-oxidising atmosphere yield carbon fibres which are highly crystalline with the C axis of the graphite crystallites preferentially alinged normal to the fibre longitudinal axis.

In a process for producing a high strength carbon fibre cloth according to the present invention, as a first step, continuous yarns of polymeric fibre material of the type referred to which have been oxidized, produced for example as disclosed in co-pending US. application Ser. No. 648,916 by heating fibres of polymeric material of the type referred to in an oxidising atmosphere at 3,541,582 Patented Nov. 17, 1970 temperatures within the range C.-250 C. and to below their melting point whilst held under tension, are woven by a conventional weaving process to provide a woven cloth of oxidized yarns and as a second step, the woven cloth of oxidized yarns is carbonised by heating in a non-oxidising atmosphere up to temperature in the region of about 1000" C. to provide a carbon fibre cloth of high strength.

As a further step, the carbon fibre cloth may be heat treated by heating the carbon fibre cloth to a temperature within the range of above the carbonising temperature and up to 3000 C. in a nonoxidising atmosphere.

Tension may be applied to the cloth during the heat treatment steps.

In one example according to the invention 1 /2 denier continuous fibres of Courtelle (Registered trademark), a polyacrylonitrile fibre containing minor proportions of other materials, were heated whilst held under tension to ensure constant length whilst in and passing through an oxidising atmosphere as disclosed in copending US. application Ser. No. 648,916 to provide black oxidised yarns. The mechanical properties of single fibres taken from the oxidised yarns produced were as follows:

Ultimate Elongation tensile at tensile strength, failure lb./sq. inch percent 43. 7X 10 19. 6 35. 7X10 l8. 9 33. 7X 10 16. 3 27. 7X10 8. 3

It will be seen from these figures that the elongation characteristics of these oxidised fibres are such as to permit the fibres to sustain the manipulating loads experienced during a normal weaving process and allow a woven cloth of oxidised polymeric material to be made.

The weave of the cloth should be sufiiciently open to allow shrinkage in the order of 12% to take place and should be such that there is a minimum of bend on the fibres where the warp and weft fibres cross each other.

Subsequent carbonising and heat treatment of a woven cloth of oxidised fibre gives a carbon fibre cloth of high strength due to the high strength and high Youngs modulus of the individual carbon fibres comprising the cloth.

In one example using 1 /2 denier Courtelle, the polymer fibre was first oxidised under tension sufficient to prevent shrinkage at a temperature of 220 C. for 4 hours. The oxidised fibre was then woven into a cloth and the cloth carbonised up to a 1000 C., the temperature being raised from 220 C.-1000 C. at a rate of about 100 C. per hour.

Twenty individual carbon fibres extracted from the carbon fibre cloth were found to have a mean ultimate tensile strength of 285 10 lb. per sq. inch and a mean Youngs modulus of 25 X 10 lb. per sq. inch.

After further heat treatment of the carbon cloth by heating up to a temperature of 2500 C. in a non-oxidising atmosphere, twenty individual carbon fibres extracted from the carbon fibre cloth were found to have a mean ultimate tensile strength of 200x10 lb. per sq. inch and a mean Youngs modulus of 50 10 lb. per sq. inch.

It will be seen that a carbon fibre cloth comprising carbon fibres having such high strength and high Youngs modulus characteristics will itself be strong and is particularly useful as a reinforcing element in a composite material.

It is to be noted that the term polyacylonitrile fibres is used by those skilled in this art to include co-polymers or ter-polymers of acrylonitrile with other monomers e.g.

3 methl methacrylate or vinyl acetate, either alone or to which have been added polymers compatible with them for example phenolic resins or Friedel-Crafts condensates. It is in this sense that the term polyacrylonitrile fibres is used throughout the specification.

We claim:

1. A process for producing a high strength carbon fiber cloth comprising a first step in which oxidized yarns of polymeric fiber material which have been oxidized by heating in an oxidizing atmosphere at a temperature within the range 100250 C. and below their melting point whilst held under tension, are woven to provide a woven cloth of oxidized yarns, and, a second step, in which the woven cloth of oxidized yarns is carbonized by heating in a non-oxidizing atmosphere up to a temperature in the region of about 1000 C. to provide a carbon fiber cloth.

2. A process for producing a high strength carbon fiber cloth as claimed in claim 1 wherein the polymeric fiber material comprises polyacrylonitrile.

3. A process for producing a high strength carbon fibre cloth as claimed in claim 1 and comprising a third step in which the carbon fibre cloth is further heated to a temperature within the range of above the carbonising temperature and up to 3000 C. in a non-oxidising atmosphere.

References Cited UNITED STATES PATENTS 2,913,802 11/1959 Barnett 28-76 3,107,152 10/1963 Ford et al. 23-2092 3,285,696 11/1966 Tsunoda 23209.1 3,412,062 11/1968 Johnson et al. 26037 FOREIGN PATENTS 1,432,042 2/ 1966 France.

EDWARD J. MEROS, Primary Examiner US. Cl. X.R. 

